The invention relates to a method of processing silver halide photographic material.
Conventional photographic paper and films are usually processed by passing a web of the material through a number of tanks containing the processing chemicals. It is usual for the web to be covered with liquid whilst in the tank, travelling through the air only when going from one tank to the next. This requires the tank to contain sufficient liquid to cover the film. To reduce the amount of liquid in the tank and to lower the effect of chemical decomposition, the spaces in the tank not occupied by the web being processed can be filled up giving, for example, a low volume thin tank (LVTT).
Another way of reducing the liquid volume is to have the web passing through a small amount of liquid, a xe2x80x98puddlexe2x80x99, in the bottom of the tank, picking up liquid on its way through, and thus a proportion of the processing takes place in the air above the tank. The web may pass through the liquid a number of times if the threaded path of the web is configured to do so. This may be a achieved by the web taking a helical path along a tank, before crossing over into an adjacent tank or by going up and down a number of times into the puddle in the general direction of movement of the web.
Another way of processing with a small amount of liquid is to have a short length of web e.g. a single film, affixed to the inside of a drum processor. Processing liquid is put in the drum such that a xe2x80x98puddlexe2x80x99 is formed at the bottom containing sufficient liquid to carry out the process. The drum is rotated such that the material is wetted as it passes through the puddle on each revolution of the drum. For most of the time in the process the web is being processed with the liquid picked up when it travels through the puddle. At the end of each process step, the processing solution may be drained from the drum and replaced with the solution for the next step.
It is known to add viscosity increasing agents to processing solutions that are to be used in lamination processes such as diffusion transfer where two webs are brought together e.g. the Polaroid peel apart process, diffusion transfer copying and plate making.
Viscosity increasing agents are often employed in xe2x80x98single-usexe2x80x99 processing where liquid is applied to the surface of a material and left until the process is complete. The high viscosity of this solution, often  greater than 1000 Cp, is require to put down sufficient chemical in one pass to complete the process. The processing liquid remains essentially stationary with respect to the web. Examples of this type of process are described in JP90014690 B (Konica) and DD98377 A (Keiler JA).
The problem encountered with the processes where the web spends a portion of its time travelling in air, is that the liquid runs back into the puddle as the web leaves it leaving only a thin layer of liquid on the surface. As reactions in the film take place, the xe2x80x98usefulxe2x80x99 chemicals in this layer are depleted by diffusion. If the web had been processed in stationary solution, a diffusion boundary layer would have built up. As these chemicals become depleted the rate of the process will be reduced increasing the processing time or causing change the sensitometry compared to a deep tank process. As the web returns to the liquid the surface layer will be renewed. Ideally the thickness of liquid carried on the surface of the film should exceed that of the diffusion boundary layer formed in the time that the web left the puddle and the time it returns to it. In this way the effects of the depletion in the surface layer will be minimised. It will be similar to that found in a deep tank with roller wipes hitting the film at the same rotation speed of the drum or the re-entry time of a continuous web.
Also there is a tendency for the web to xe2x80x98de-wetxe2x80x99 in the air above the liquid and the surface liquid either forms drops or runs to the middle causing an excess of liquid is some places and a deficiency in others. This leads to uneven processing.
It has been found that the run back and de-wetting can be reduced by increasing the viscosity of the processing solutions sufficiently to increase the amount of liquid adhering to the film, such that its thickness approaches that of the boundary layer thickness.
The invention provides a method of processing a silver halide photographic material which comprises passing the material through a processing solution repeatedly at a temperature suitable for processing, the material spending the major part of the processing time out of the liquid, wherein said processing solution has a viscosity from 0.7 to 5 cP at the processing temperature.
The invention allows more rapid processing in all processes, particularly in processes where diffusion control is important e.g. fixing.
More even processing is achieved as the liquid is more likely to be retained as a continuous film over the whole of the web""s surface.